The long-term objective of this proposal is to develop mechanism-based therapeutic strategies for the treatment of human head and neck squamous cell carcinoma (HNSCC). The sphingolipid ceramide, a proposed tumor suppressor lipid, mediates anti-proliferation in response to chemotherapeutic agents in human cancers, including HNSCC. Data here demonstrate that the levels of only one ceramide, C18-ceramide, were significantly lower in about 80% of the tumor tissues of the patients with HNSCC as compared to their adjacent normal tissues. Induction of longevity assurance gene 1 (LAG1), identified as the first regulator of life-span, which is involved specifically in the synthesis of C18-ceramide, suppressed growth of HNSCC cells via apoptosis, and the modulation of telomerase activity. These data suggested the overall HYPOTHESIS that C18:0 ceramide plays a key role in the regulation of growth, and response to chemotherapy in HNSCC. Two specific aims are proposed: Specific Aim 1) Determine the role of C18-ceramide by LAG1 activity in the regulation of growth in HNSCC. This specific aim will concentrate on evaluating the novel hypothesis that LAG1 via C18-ceramide regulates growth of HNSCC cells via modulation of telomerase and induction of apoptosis; a) determine the mechanisms of down-regulation of C18-ceramide in tumors obtained from patients with HNSCC; b) determine the role of increased generation of C18 ceramide in the inhibition of growth by modulation of telomerase and/or induction of apoptosis in HNSCC cell lines; and c) determine the mechanisms by which LAG1 via C18- ceramide i) inhibits telomerase activity; and ii) induces apoptosis in these cells. Specific Aim 2) Establish the role of LAG1 via C18 ceramide in the growth suppression functions of anti-cancer agents in HNSCC. This specific aim will test the hypothesis that activation of LAG 1, resulting in increased generation of C18-ceramide, in response to specific chemotherapeutic agents leads to growth suppression of HNSCC cells via modulation of telomerase and induction of apoptosis; a) define the subset of chemotherapeutic agents (alone or in combination) which induce LAG1, and generation of C18-ceramide; b) determine whether LAGl/C18-ceramide pathway is sufficient and/or necessary for chemotherapy-induced suppression of cell growth; and c) test the corollary that attenuation of C18-ceramide via over expression of glucosylceramide synthase and/or ceramidase - which increase the clearance of ceramide, result in the development of resistance to chemotherapy-induced cell death. These experiments will help identify roles and downstream targets of specifically LAG1 via C18-ceramide in chemotherapy-induced suppression growth of HNSCC.